This is my first post on the forums, and I'm working on my horizontal stabilizer for my RV-9A. As is tradition, I've hit a couple of snags fabricating my HS-908 attach angles. I had to remake one, but I think I have the outside dimensions right. I've started drilling holes, and I used a tip from the forums for getting the top center holes lined up, at least vertically (clamp both angles to a piece of scrap aluminum and use one as a drill guide).

I drew Sharpie lines to mark where I wanted the remaining holes to be, and I used my pin punch to make a small divot where I wanted the hole to be centered. I used a new #40 bit, centered it in the divot, and drilled slowly, but the holes came out slightly off from where I wanted them to be.

I have what I think (if I'm reading my technical reference correctly) is adequate edge margin (all greater than 0.250", assuming the electronic calipers I got from Lowe's can be trusted), but the holes are not uniformly spaced among themselves, and some holes are closer than the 0.500" called for on DWG 3. I measured the distances between them and added the hole diameters; the distances (center to center) range from 0.464" to 0.565" (remarkable that it's almost exactly 0.100" from smallest to largest!). I think the minimum distance is three times the diameter of the rivet (again, assuming I'm reading the technical reference right), and for these AN470AD4 rivets that should be 0.375", so the 0.464"-0.565" range should be fine.

I could remake the angle, but I don't know for sure that I'd make a better one if I did. And part of this task is learning what's serviceable and what to redo. I know once I match-drill the HS front spar and doubler plate, I'm committed to either accepting the angle or buying a new spar half and doubler plate.

I'd appreciate any thoughts or suggestions! Also, any suggestions for getting the other angle drilled right the first time?

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Will, building an RV-9A
Horizontal stabilizer in progress
Donated September 2018

Will,
I had sort of the same issue with the drillings. Trying to get 9 holes equispaced like that perfectly is very hard to do manually, and is the stuff of a CNC machine. I've only just started work on the empennage and I think in the end I made about 5 brackets before I had two that were good. The most important thing (in my opinion and someone more qualified might change this) is to have the two top row centre holes match-drilled as these then set the spacings to the fuselage deck. The remaining 8 holes exact position isn't super critical so long as you have the spacings above minimum.

My advice is when you make the second one, clamp it to the first so the bottom ledge of the angle is aligned, then drill both of the alignment holes together. I didn't do this first up, and ended up with one angle about 0.5mm short of the other.

To reiterate, the first hole is used for overall alignment and precision is important, the remaining 8 not so much. The holes shown above look fairly even and are much better than my first attempt. I butchered the riveting of the first set and butchered even more the attempted removal of bad rivets and so choose to replace the spar. The 4" squeezer yoke worked, the 3" yoke did not.

So after I posted this, I reached out to Van's, and the word was (in essence) "It's OK. It doesn't have to be perfect." So I drilled my holes in the spar and doubler and got on with life. I did get those top center holes lined up pretty good -- when I clecoed the spar halves, doubler, and attach angles, it was dead-on level.

Thanks for the words of encouragement, Geoff and Eric. Now on to the skins!

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Will, building an RV-9A
Horizontal stabilizer in progress
Donated September 2018

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